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https://issues.apache.org/jira/browse/SAMZA-503?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14278102#comment-14278102
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Roger Hoover commented on SAMZA-503:
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[~closeuris], thanks for investigating. If this is how it works, then it seems
to explain why it took so long to move from 0. I guess it may have taken
10mins to fill up the BroxyProxy cache in my test.
If the intent of the metric is to show the difference between the latest offset
of the incoming stream and that of the BrokerProxy, then the name
"messages-behind-high-watermark" is very misleading. Maybe it should be
"prefetch-messages-behind-high-watermark" and the other lag metric would be
"commited-messages-behind-high-watermark".
>From a user's perspective, the "commited-messages-behind-high-watermark" is
>really what I care about.
> Lag gauge very slow to update for slow jobs
> -------------------------------------------
>
> Key: SAMZA-503
> URL: https://issues.apache.org/jira/browse/SAMZA-503
> Project: Samza
> Issue Type: Bug
> Components: metrics
> Affects Versions: 0.8.0
> Environment: Mac OS X, Oracle Java 7, ProcessJobFactory
> Reporter: Roger Hoover
> Assignee: Yan Fang
> Fix For: 0.9.0
>
>
> For slow jobs, the
> KafkaSystemConsumerMetrics.%s-%s-messages-behind-high-watermark) gauge does
> not get updated very often.
> To reproduce:
> * Create a job that processes one message and sleeps for 5 seconds
> * Create it's input topic but do not populate it yet
> * Start the job
> * Load 1000s of messages to it's input topic. You can keep adding messages
> with a "wait -n 1 <kafka console producer command>"
> What happens:
> * Run jconsole to view the JMX metrics
> * The %s-%s-messages-behind-high-watermark gauge will stay at 0 for a LONG
> time (~10 minutes?) before finally updating.
> What should happen:
> * The gauge should get updated at a reasonable interval (a least every few
> seconds)
> I think what's happening is that the BrokerProxy only updates the high
> watermark when a consumer is ready for more messages. When the job is so
> slow, this rarely happens to the metric doesn't get updated.
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